LIDAR with spatial light modulator

ABSTRACT

A spatial light modulator (SLM) has an array of pixels configured to modulate light in patterns responsive to first control signals. The modulated light forms at least one patterned light beam in a field of view. An illumination source is optically coupled to the SLM. The illumination source is configured to illuminate the array of pixels, responsive to second control signals. Circuitry is coupled to the SLM and to the illumination source. The circuitry is configured to provide the first control signals to the SLM and the second control signals to the illumination source. At least one detector is configured to detect a reflection of the patterned light beam in the field of view.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/202,315 filed Jul. 5, 2016, which claims priority to U.S. ProvisionalPatent Application Ser. No. 62/188,035, filed Jul. 2, 2015, theentireties of both of which are incorporated herein by reference.

BACKGROUND

This relates generally to light detection and ranging systems. The term“LIDAR” is a portmanteau of the words “light” and “radar” created todescribe systems using light for ranging and depth imaging systems. Morerecently, the term (LIDAR or “lidar”) forms an acronym for “LightDetection and Ranging.” LIDAR systems form depth measurements and makedistance measurements. In LIDAR systems, a source transmits light into afield of view and the light reflects from objects. Sensors receive thereflected light. In some LIDAR systems, a flash of light illuminates anentire scene. In the flash LIDAR systems, arrays of time-gatedphotodetectors receive reflections from objects illuminated by thelight, and the time it takes for the reflections to arrive at varioussensors in the array is determined. In an alternative approach, a scansuch as a raster scan can illuminate a scene in a continuous scanfashion. A source transmits light or light pulses during the scan.Sensors that can also scan the pattern, or fixed sensors directedtowards the field of view, receive reflective pulses from objectsilluminated by the light. The light can be a scanned beam or movingspot. Time-of-flight computations can determine the distance from thetransmitter to objects in the field of view that reflect the light. Thetime-of-flight computations can create distance and depth maps. Thedepth maps are displayed. Light scanning and LIDAR have been used in avariety of applications, including: ranging; metrology; mapping;surveying; navigation; microscopy; spectroscopy; object scanning; and inindustrial applications.

Recently LIDAR applications also include security, robotics, industrialautomation, and mobile systems. Vehicles use LIDAR navigation andcollision avoidance systems. Autonomous vehicles and mobile robots useLIDAR.

In conventional mechanically scanned LIDAR systems, a rotating mirror ormirrors can cause a laser beam to scan the scene in the field of view.Sensors detect light reflected from objects in the field of view bybackscattering. The fixed scan patterns result from mechanicallyrotating a laser or from mechanically rotating a mirror reflecting lightfrom a laser or collimator fed by a laser. These conventional systemsinclude a variety of mechanical components such as motors, rotors, andmoving mirrors that have substantial power and weight requirements,require maintenance, and are subject to failure and require repair.

An example LIDAR application is autonomous vehicles. Currentcommercially available LIDAR systems for autonomous vehicle applicationsinclude many components and moving parts. Mechanical motors, rotators,and housing arranged for mounting the system on vehicle roofs arerequired. U.S. Pat. No. 7,969,558, issued Jun. 28, 2011, entitled “HighDefinition LIDAR System,” assigned to Velodyne Acoustics, Inc.,describes a vehicular system having eight assemblies of eight laserseach to form a sixty-four laser/detector assembly mounted on a vehiclerooftop. The lasers and detectors mount in a rotating housing thatrotates at up to 20 Hz. Motors and rotating mechanical parts provide thehigh-speed rotation. Each of the eight assemblies includes multiplelasers and detectors. Such systems are high in cost, are mechanicallyand electrically complex, require special power and maintenance, and arephysically large and affect the appearance of and the exterior surfacesof the vehicle.

SUMMARY

A spatial light modulator (SLM) has an array of pixels configured tomodulate light in patterns responsive to first control signals. Themodulated light forms at least one patterned light beam in a field ofview. An illumination source is optically coupled to the SLM. Theillumination source is configured to illuminate the array of pixels,responsive to second control signals. Circuitry is coupled to the SLMand to the illumination source. The circuitry is configured to providethe first control signals to the SLM and the second control signals tothe illumination source. At least one detector is configured to detect areflection of the patterned light beam in the field of view.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a conventional LIDAR system.

FIG. 2 illustrates a conventional LIDAR system in a vehicle application.

FIG. 3 illustrates a raster scan pattern.

FIG. 4 illustrates a conventional projection system using a DMD.

FIGS. 5A and 5B illustrate operations of a digital micromirror in aprojection system and a corresponding pupil diagram.

FIGS. 6A and 6B illustrate two different mirror orientations.

FIG. 7 illustrates an example operation.

FIGS. 8A, 8B and 8C illustrate an image pattern, a correspondingdiffraction pattern, and a corresponding image formed using thediffraction pattern, respectively.

FIG. 9 illustrates a method of computing a binary diffraction pattern.

FIG. 10 is a block diagram of a system of example embodiments.

FIG. 11 illustrates an example of generating an image using diffraction.

FIG. 12 is another block diagram of a system of example embodiments.

FIG. 13 is a block diagram of the system of FIG. 12 in a scan operation.

FIG. 14 is a diagram of scan patterns.

FIG. 15 illustrates a scanning pattern on objects in a field of view.

FIG. 16 illustrates an adapted scanning pattern on objects in a field ofview.

FIG. 17 is a block diagram of the system of FIG. 13 in an adaptive scanoperation.

FIG. 18 is a flow diagram of a method of generating diffractionpatterns.

FIG. 19 is a flow diagram of a method of forming diffraction patterntemplates.

FIG. 20 is a flow diagram of a method of using stored diffractionpatterns to form a scan pattern.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Corresponding numerals and symbols in the drawings generally refer tocorresponding parts unless otherwise indicated. The drawings are notnecessarily drawn to scale.

The term “coupled” may also include connections made with interveningelements, and additional elements and various connections may existbetween any elements that are “coupled.”

Example embodiments provide ranging and/or depth measurement lightdetection systems using digital micromirror devices (DMDs). DMDs displaydiffraction patterns illuminated to provide scan patterns. Detectorssense the scan pattern light reflected from objects in the field ofview. Time-of-flight calculations determine distance or depthinformation. Example embodiments include systems where diffractivepatterns are displayed using the DMD. At least one coherent light sourceilluminates the DMD. The coherent light source can be a laser. The lightcan be pulsed. At a predetermined distance in the field of view of thesystem, an image such as a pattern, a spot or multiple spots form byinterference of the light waves traveling from the DMD. Sensors detectreflections from the scan patterns that occur due to backscattering fromobjects. Distance to the objects can be determined using time-of-flightcomputations. In some alternative example arrangements, a flashillumination over an entire scene occurs, and then an array ofphotodetectors can integrate reflected light signals over time. A numberof iterative or non-iterative algorithms can generate the diffractiveimages. In some of the algorithms, Fourier transforms simulate thedesired far field image. In an example, inverse Fourier transforms cancompute the diffraction patterns that are appropriate to form desiredscanning patterns in the far field. After computing the complex inverseFourier transform data, the system performs filtering of the data andquantizing of the complex inverse Fourier transform data. The systemarranges binary data corresponding to the diffractive pattern fordisplaying the diffractive pattern using the DMD. In an example, aplurality of two dimensional diffraction pattern templates needed toform a desired scanning pattern are stored for retrieval. The patternscan include raster scanning patterns. In scanning the field of view, thediffractive pattern templates are displayed using the DMD in sequencesdesigned to create the desired scanning pattern. In alternativeexamples, real time computing is used to compute the two dimensional DMDdiffraction pattern data as needed. The real time computation outputsvideo data to display a scanning sequence using diffractive patterns onthe digital micromirror device. In a scene adaptive example, the systemresolution increases in the scanning pattern for a selected portion ofthe field of view with an object of interest. Using coarse resolutionover a part of the scene with finer resolution for an area of interestin the scene improves performance. By leaving a portion of the scanpattern in a coarse resolution, processing time improves. By increasingresolution in an area of interest, system performance and resolutionimproves. Here the resolution can be defined by the number of individualbeam positions covered during the scan or the divergence of the beamsthemselves.

FIG. 1 illustrates in a block diagram a conventional LIDAR systemoperation. In FIG. 1, system 100 includes a laser (or other lightsource) 101 arranged to illuminate a mirror 103. A rotating mount 106rotates mirror 103 so that the laser beam movably travels across thefield of view. In FIG. 1, a human FIG. 105 is in one part of the fieldof view, and a tree 113 is in another part of the field of view. Thetree 113 and the human FIG. 105 are located at different distances frommirror 103.

When a pulse of laser energy enters the field of view from the surfaceof mirror 103, reflective pulses appear when the laser light illuminatesan object in the field of view. These reflective pulses arrive at mirror109 that can also movably rotate on a rotating mount 108. The reflectivepulses reflect into a photodetector 111. The photodetector 111 can beany of a number of photodetector types; including avalanche photodiodes(APD), photocells, and/or other photodiode devices. Imaging sensors suchas charge-coupled devices (CCDs) can be the photodetectors.

As shown in FIG. 1, the photodetector 111 receives reflective lightpulses. Since the time the transmit pulses are transmitted from laser101 onto mirror 103 is known, and because the light travels at a knownspeed, a time-of-flight computation can determine the distance ofobjects from the photodetector. A depth map can plot the distanceinformation.

FIG. 2 illustrates in a block diagram an example vehicle mounted LIDARsystem 200 such as in conventional autonomous vehicle applications. InFIG. 2, a car 201 includes a mechanically rotating LIDAR system 203mounted on the rooftop of the vehicle. The rotating LIDAR systemtransmits laser pulses and measures reflections from objects around thesystem using time-of-flight calculations based on the speed of light.LIDAR systems for autonomous vehicles are available from Velodyne Lidar,Inc. An example system, the HDL-64, has sixty-four lasers arranged withcorresponding detectors mounted in a rotating housing with a rotatormotor that rotates the housing at up to 20 Hz. This system requirespower to the motor, the many lasers, and the many detectors, as well asrequiring substantial physical space on the roof of the vehicle.

FIG. 3 depicts in a simple diagram a representative pattern for scanninga scene using light. In the example of FIG. 3, a “raster” pattern shownby line 301 proceeds horizontally along a line position from one side ofa field of view to the opposing side. The raster pattern returns to scanacross the scene at another horizontal position vertically displacedfrom the first row. The pattern 300 shown in FIG. 3 illustrates a commonscanning pattern for a single spot or beam. However, the variousembodiments can use any number of alternative scanning patterns.

An important technology for light processing is DLP® technology fromTexas Instruments Incorporated. TI DLP® home and cinema projectors,televisions, and sensors are in widespread use. These systems use one ormore spatial light modulators having digital micromirror devices (DMDs),a reflective spatial light modulator technology developed by TexasInstruments Incorporated. In a DMD, a two dimensional array of mirrorsis formed over a hinged torsional tilting mechanism. Electrical signalscontrol the torsion to tilt the mirrors. The mirrors each have acorresponding data storage unit that are each individually addressable,and each micromirror can be switched between two states many thousandsof times per second. DMD devices available from Texas Instruments caninclude many thousands and even millions of the micromirrors and cansupport various video resolutions. DMDs are reliable and robustespecially as a diffractive beam scanner, because even if substantialportions of the micromirrors become inoperable, the high number andsmall size of the digital micromirrors provide inherent redundancy. DMDshave proven to be highly reliable, long life, solid-state devices forprocessing light. Because a DMD reflects light and each micromirror hasan ON state and an OFF state, the DMD acts as a binary amplitudemodulator.

FIG. 4 depicts in a simplified block diagram a DMD used in aconventional image projector system. In system 400, a single lightsource 407 and illumination optics 409 direct light from the lightsource onto the face of a DMD 401. Some systems use multiple lightsources such as red, green and blue light sources. Some color lightsystems use color wheels to create colored light from a single lightsource. Some systems use multiple DMDs. DMDs such as DMD 401 aremanufactured using micro-electromechanical system (MEMS) technologybased in part on semiconductor device processing. An array ofmicromirrors 403 is disposed over a semiconductor substrate 405. In anexample, the micromirrors include aluminum faces and are each mounted ona hinged torsion mechanism. The micromirrors 403 attach to a torsionhinge and can be tilted using electronic signals applied to electrodesthat control a tilt by applying torsion to pivot the micromirrors aboutan axis. In an example DMD device, a two dimensional array of thousandsor perhaps millions of the micromirrors form a WGA, XGA, 720p, 1080p orhigher resolution imaging device. The micromirrors 403 reflectillumination light from the illumination optics 409 to a projection lens406. A beam of light projects from the system 400. By displaying animage using the DMD and illuminating the DMD micromirrors, the reflectedbeam of light can include an image for display on a surface such as ascreen or wall. The micromirrors 403 are individually addressable, andeach has an associated storage memory cell that determines the state ofthe micromirror during an active illumination period.

The micromirrors 403 each have three individual states: a first “ON”state; a second “OFF” state; and a third “FLAT” state. In the ON state,the micromirrors 403 in FIG. 4 tilt in a first position away from theFLAT position. The tilt occurs due to signals on an electrode that causethe torsion hinges to flex. In system 400, the micromirrors 403 in theON state reflect incoming light from illumination optics 409 outwards tothe projection lens 406. In the OFF state, the micromirrors 403 tilt toa different position. In this example arrangement, mirrors in the OFFstate reflect the light away from the projection lens 406. In somearrangements, the OFF state light reflects to a “light dump” (not shown)or thermal energy collector. By varying the tilt positions usingelectrical control signals, each of the micromirrors 403 can directreflected light to the projection lens 406. The FLAT state is theposition the micromirrors take when no power is applied to the DMD andis currently not used for any application. In at least one example, theFLAT position is 0 degrees, and a DMD from Texas InstrumentsIncorporated has an ON state tilt of about +12 degrees and an OFF statetilt of about −12 degrees. Other DMD devices provide different tiltangles, such as +/−10 degrees, or +/−17 degrees.

FIGS. 5A and 5B further illustrate the operation of a micromirror in aconventional projector incorporating a DMD as a spatial light modulator.In FIG. 5A, projection system 500 incorporates a single illustrativemicromirror 522. In the actual projector device, the DMD will havethousands or millions of micromirrors arranged in a two dimensionalarray. FIG. 5A illustrates the various positions of the micromirror 522.In the ON state, the micromirror 522 is at a first tilted positionconsidered ON, such as +12 degrees from the vertical or FLAT position.The illumination source 524 is at an angle of −24 degrees from the zerodegree (with respect to the vertical) position, so that the zero degreeangle is aligned with the projection lens 528. When reflecting from thesurface of a mirror, the angle of incidence (AOI) of the incoming lightis equal to the angle of reflection (AOR) of the reflected light;therefore, for a +12 degree tilt, the −24 degree angle for theillumination source results in reflected light at the zero degreeposition, as shown in FIG. 5A. The cone of reflected light ON STATEENERGY shows the reflected light directed outwards from the micromirror522 at the zero degree position. When the micromirror 522 is in the ONstate, the light from the illumination source 524 reflects as the coneof light labeled ON STATE ENERGY at zero degrees into the projectionlens 528. The projected light projects from the projection system 500.The micromirror 522 is in a FLAT state when the DMD is unpowered. Whenthe micromirrors are in the FLAT state in a video projection system, theillumination source is also usually unpowered. The micromirror 522 cantilt to an OFF state. In the OFF state position, the micromirror 522 isat a second tilt position at an angle of −12 degrees from the FLATposition. In the OFF state, the illumination light that strikes themicromirror reflects away from the projection lens 528, and is outputinto a light dump 526. Light dump 526 can be a heat sink that dissipatesheat from the light. In this example, when the micromirror 522 is in theOFF state, the reflected light does not exit the projection system.

In conventional projection systems, the FLAT state of the micromirror522 is not used when the DMD is active. All of the DMD micromirrors moveto the FLAT state when the DMD device powers off. The FLAT position is a“parked” or “safe” position for the micromirror 522.

FIG. 5B illustrates a pupil diagram 529 for the projection system 500,including the pupil positions for the three mirror states (OFF, FLAT,ON) and the pupil position of the light source (LAMP). The pupil diagram529 shows the approximate position of micromirror 522 (FIG. 5A) centeredin the ON state pupil. In pupil diagram 529, the illumination source fora conventional projector is at pupil position LAMP. The ON pupilposition is adjacent and above the LAMP pupil position. The FLAT pupilposition is adjacent and above the LAMP pupil position, and the OFFpupil position is adjacent and above the FLAT pupil position. Asillustrated in the pupil diagram, the positions of the pupils center ona vertical line due to the micromirror having a single action hinge.This type of DMD is commercially available and sold by Texas InstrumentsIncorporated. For example, the Texas Instruments Incorporated deviceDLP3000 has an array of 608×684 micrometer sized mirrors, equating tomore than 400,000 micromirrors. The DLP3000 is one example DMD but manydifferent DMD devices are available from Texas Instruments Incorporated.

DMDs can vary in mirror size, array size, tilt angle, and mirrororientation. FIGS. 6A and 6B illustrate two different mirrororientations. In the DMD shown in FIG. 6A, the mirrors or pixels areoriented in the “Manhattan” or “square pixel” fashion with the edgesaligned vertically with column spaces between the mirrors, and edgesaligned horizontally with row spaces between mirrors. As shown in FIG.6A, the tilt angle for the two example mirrors 603, 605 in thisorientation is on the diagonal. This results in an “off axis”requirement for the light source in a projector. The illumination light(labeled “From Light Source”) has to come from a point above (or below)the micromirror array and has to be angled with respect to it. Indesigning a system around the DMD of FIG. 6A, the housing has to havesome vertical spacing above (or below) the DMD device as well ashorizontal spacing for projection optics in front of the DMD arranged toproject the image from the DMD. In FIG. 6A, when the mirrors are in theON state the light reflects toward a lens; in contrast, when the mirrorsare in the OFF state the light reflects away from the lens to a lightabsorber.

In FIG. 6B, a two adjacent mirrors in a diamond pixel mirror array areillustrated. Recent DMD devices released by Texas InstrumentsIncorporated provide two dimensional micromirror arrays with the diamondorientation. In this orientation, the mirrors tilt ON and OFF around avertical axis, and the edges are arranged diagonally with respect tocolumns and rows. Because the tilt angles for ON and OFF states aresymmetric about a vertical axis, the illumination source and the DMD canbe in the same horizontal plane. The illumination source no longer hasto be placed above or below the DMD (“off axis.”) In the ON state, thelight enters the DMD from the side and reflects forward from the DMD toa lens. In the OFF state, the light reflects to the opposite side to alight absorber. All of the light paths are in the same horizontal plane.This aspect of the diamond DMD allows for a more compact system as thelight source is in the same plane, horizontally, as the DMD and theprojection lens. Compact projectors, such as handheld portableprojectors and pico projectors for incorporation in other portabledevices such as tablets and mobile phones, can use the diamond pixelDMDs. Additional signal processing maps the pixel data for an imageframe onto the diamond DMDs but this signal processing is compatiblewith the type of processors typically used in digital light processingsystems that use DMDs.

In addition to the DMDs described herein above, Texas InstrumentsIncorporated also offers DMDs with a complex tilt mechanism described as“tilt and roll pixel” or TRP. The example embodiments can also use theseTRP DMDs. TRP DMDs feature a tilt angle of +/−17 degrees. Illuminationcan begin on one side, with the ON state output in front of the DMD andwith the OFF state being below or above the DMD. A commerciallyavailable part DLP3114 manufactured by Texas Instruments Incorporated isan example of a TRP DMD device that can be used in the variousembodiments

In projection systems using a DMD, illumination optics provide a cone oflight onto the DMD while the mirrors tilt “on” or “off” to provide theimage to be displayed. Projection optics then focus that image onto asurface for display. Various display systems use DMDs as projectors.Applications include: theatre and conference room projectors thatdisplay on a wall or screen; rear projection televisions that projectonto a display screen; home projectors; sales or presentationprojectors; hand held and pico-projectors; heads up displays foraviation, marine and automotive applications; virtual reality andwearable goggles; personal video players displays; and smart glassesdisplays. Each of these applications uses the DMD as a reflectivespatial light modulator.

The two-dimensional array of micromirrors in a DMD can act as adiffraction grating. The pitch of the DMD devices varies from a fewmicrons to about fourteen microns. The pitch of these devices is smallenough, when compared to the wavelengths of coherent light sources suchas lasers, to exhibit significant diffraction. In projection systems,the diffraction effects are not desirable and these effects areminimized by optical design.

In the example embodiments, a DMD displays a diffractive pattern, anddoes not display a projection image. Diffraction changes the directionand distribution of light due to traversing apertures such as an openingor slit. The DMD mirrors and the spaces between the DMD mirrors providea natural diffraction grating. Further, diffractive patterns displayedusing the DMD can create desired patterns in a far field image plane.These patterns result from interference between wavefronts of lighttraveling away from the diffractive pattern on the DMD. The imagepatterns in the far field can be almost unlimited in variety. A singleDMD and a single illumination source can form many patterns in the farfield image plane.

To illustrate the diffractive characteristic of a DMD, FIG. 7illustrates in a block diagram a far field image result obtained byilluminating an entire DMD micromirror array with a laser illuminationsource. In FIG. 7, a system 700 operates by directing the output of alaser 705 onto the mirror surfaces of DMD 703. Afocal lenses 707 and 708collect the output light and provides an afocal lens correction toilluminate a larger field of view than can be illuminated in a “lensless” system. However, the use of the afocal lenses 707 and 708 is notrequired, and in alternative embodiments, the system can be “lens less.”The far field image shown as 709 in FIG. 7 is a pattern of spots with abrighter spot in the center, and the pattern of spots symmetricallysurrounds the center spot. The pattern 709 illustrates that the DMD isacting as a diffraction grating for the illuminating laser.

An embodiment system can use the diffraction properties of the laser andthe DMD to form arbitrary patterns at the far field image plane. Forexample, a pattern of spots can form as shown in FIG. 7. Further, bydisplaying a particular diffraction pattern using the DMD, the locationsof the spots can be any arbitrary position in the field of view of thesystem. Because the DMD can rapidly switch between different diffractivepatterns, a sequence of patterns can be displayed using the DMD, witheach diffraction pattern being illuminated by the laser. By continuingto display different patterns in the sequence, a scanning pattern ormoving spot pattern forms at the far field. In this example system, theDMD is acting as a hologram display. The hologram pattern can cause abeam or beams. The beams can result in reflections from objects locatedat distances from a few centimeters to one hundred meters or up toseveral hundred meters from the DMD and illumination source.

Because the patterns are hologram or diffraction patterns and notrecognizable images, focused optical elements are not required in theembodiments. However, as described hereinabove the embodiments caninclude afocal lens elements to expand the field of view covered by thelight pattern. Range of the system can be between a few centimeters toseveral hundred meters. A rapidly pulsing laser can illuminate the DMD.The laser can be at low power levels and with short pulse durations thatare “eye safe” so that a viewer will not suffer eye damage if the laserlight strikes an observer's eye. The system can use infrared and otherillumination frequencies.

An example system using a DMD as a diffraction pattern generator orhologram display device is described in a paper entitled “Digital micromirror device as a diffractive reconfigurable optical switch fortelecommunication,” by Blanche et. al., Journal ofMicro/Nanolithography, MEMS and MOEMS, Vol. 13 (1), January-March 2014,pp. 011104-01-011104-05, (hereinafter, “Blanche et. al.”) which ishereby incorporated by reference in its entirety. In Blanche et. al.,the authors demonstrate that a diffraction pattern on a DMD can producean image at a desired point in an image plane. In an example systemdescribed in Blanche et. al., spot patterns input data to optical fibersin an optical switch. FIG. 8A shows an example desired pattern describedin Blanche et. al., a logo of Texas Instruments Incorporated, known asthe “TI bug.” In FIG. 8B the DMD pattern needed for producing the imageby diffraction is illustrated as it would be displayed using a twodimensional DMD array. Note that the pattern in FIG. 8B is not a visibleimage of the logo and it is clear from FIG. 8B that the DMD is notprojecting images in a conventional manner. FIG. 8C is an illustrationshowing the resulting holographic image that results from a laserillumination of the DMD array of FIG. 8B. Note that a bright spot due tothe zero order energy, analogous to a DC component of an electronicsignal, appears positioned at the center of the image. This zero ordercomponent will be present for each diffraction pattern because of thefact that the DMD can only modulate light intensity and not phase. Atthe upper left of FIG. 8C is the first order component, which reproducesthe desired image. The resulting image also has a second first ordercomponent image at the lower right portion of FIG. The conjugate firstorder image is flipped about the zero order spot. Each image formedusing a diffraction pattern will also have a conjugate image and a zeroorder spot.

As can be seen from the diffractive pattern shown in FIG. 8B, thediffraction or hologram imaging system is not projecting an imagethrough the DMD array using conventional optical projection. The patternat the far field image plane and the diffraction pattern displayed usingthe DMD can be related mathematically by a Fourier transform. Whenilluminated by a coherent source the diffraction pattern produceswavefronts that interfere constructively and destructively correspondingto the diffracted light. The desired image appears at a plane somedistance from the DMD. In the embodiments, a variety of diffractionpatterns can display on a DMD array in a sequence to form arbitrary anddesired scan patterns at some distance.

The relationship between the diffraction pattern on the DMD and theresulting pattern at a position in the field of view can be described interms of a two dimensional Fourier transform. Because the diffractionpattern and the resulting image at the far field plane are related by atwo-dimensional Fourier transform, in the embodiments where a scanpattern is needed, algorithms for generating these diffractive patternstypically use Fourier transforms.

Some fast algorithms for generating diffractive patterns or hologramsfor display on a DMD are described in a paper entitled “Fast algorithmsfor generating binary holograms,” authored by Stuart et al.,arXiv:1409.1841[physics.optics], 5 Sep. 2014, (hereinafter, “Stuart et.al.”) which is hereby incorporated by reference herein in its entirety.In Stuart et. al., the fast algorithms include an ordered ditheringalgorithm and a weighted Gerchberg-Saxton algorithm. The embodiments canuse additional algorithms to develop diffraction patterns. An examplealgorithm includes identifying a far field image pattern to be createdin the field of view; zero padding the image pattern; and taking theinverse Fourier transform of the zero padded pattern using a fastFourier transform. The method continues by quantizing the resultingcomplex IFFT data to get a binary pattern for display using the DMD, andsubsampling the binary pattern to arrange it for the particular DMDmirror orientation. By simulating the far field image using FFTs, andobserving the resulting far field image, recursive improvements canadjust the diffraction pattern until the desired far field imageresults. These recursive improvements can compensate for device specificvariations in mirror alignment and flatness, for example, to obtain thecorrect far field image without modifying the DMD.

FIG. 9 depicts in a block diagram 900 the operation of an example methodfor forming diffractive patterns for display using the DMD. FIG. 9 showsa desired pattern for a far field image, “Pattern Image” 901. One simplemethod of creating a DMD pattern that produces the desired far fieldimage 901 is to apply an inverse fast Fourier transform (IFFT) to theimage. To compute the IFFT efficiently, various computing techniques canbe used, such as a discrete fast Fourier transforms, or DFFT. Processorsoptimized for DFFT computations, such as co-processors, digital signalprocessors, and vector processors can compute the inverse DFFT. As shownin FIG. 9, the result is a two-dimensional array labeled “Complex IFFTImage” 903. The Complex IFFT Image 903 has no visible relationship tothe Pattern Image 901. The Complex IFFT image includes components thatare not of binary values. To form a corresponding diffractive patternfor display using the DMD, which is a binary amplitude modulator withthe binary states ON and OFF, the system performs additional processing.This processing can include quantization or binarization of the ComplexIFFT Image 903 to allow it to display on the binary DMD. Several methodscan be used to create a binary diffractive image that produces a desiredfar field image, such as methods described by Stuart et. al., describedhereinabove. In addition, the system maps the quantized diffractionpattern data to match the data to the selected orientation type of DMD.If the DMD is a square pixel or “Manhattan” mirror orientation, thesystem performs one type of mapping. If the DMD is a diamond pixelorientation DMD, the system performs a different mapping to map thatdata onto the DMD. In the embodiments, the methods compute a diffractionpattern for display using the DMD that will produce the desired farfield image.

Iterative optimization steps can better match the far field image to thedesired image. In an example embodiment, the Gerchberg-Saxton algorithmcan be used as an iterative algorithm. FIG. 9 illustrates theoptimization process by the “Iterative Optimization” path 907. Thisiterative process can continue for each desired pattern to obtain acorresponding diffractive pattern for display using the DMD.

Because the diffraction pattern is a two-dimensional data array fordisplay using the DMD, the patterns can be stored in memory asdiffraction pattern templates. Additional patterns can be stored inmemory in a system for retrieval and display. The processing needed tocompute the diffraction patterns using the inverse Fourier transform canbe “offline” or performed during a system calibration process, and it isnot necessary to design a system that can compute these diffractionpatterns in real time or in the field. However, in an alternativeexample, real time processing can compute the diffractive patterns, andthis approach avoids storing all of the possible diffractive patternsneeded in a memory.

FIG. 10 depicts in a simple circuit block diagram a typical arrangement1000 for use with the embodiments. A microprocessor, mixed signalprocessor, digital signal processor, microcontroller or otherprogrammable device 1011 executes instructions that cause it to outputdigital video signals DVO for display. A variety of sources may providethe digital video signals labeled DVI in the figure. In the embodiments,a system can perform the inverse Fourier transforms describedhereinabove to produce the DVI data needed for diffractive patterns inreal time. In an alternative arrangement, the DVI data can come fromstored diffraction pattern templates computed before operation of thesystem, or in a calibration operation during manufacture of the system.FIG. 10 shows an optional memory 1013 for storing diffraction patternscoupled to DSP 1011. Dynamic memory (DRAM), static random access memory(SRAM), non-volatile read write memory such as EEPROM, FLASH, EPROM andother data memory types can be used to store the diffraction patterns.The processor 1011 couples to a digital DMD controller circuit 1003.Digital DMD controller circuit 1003 is another digital video processingintegrated circuit. In an example, digital DMD controller circuit 1003is a customized integrated circuit or an application specific integratedcircuit (ASIC). FIG. 10 shows an analog circuit that manages power andLED illumination referred to as the “power management integratedcircuit” (PMIC) 1015. PMIC 1015 controls the intensity and power to thecoherent light source laser 1009. The DMD controller circuit 1003provides digital data to the DMD 1001 for modulating the illuminationlight that strikes the DMD surface. PMIC 1015 provides power and analogsignals to the DMD 1001. The light rays from the illumination source1009 travel to illumination components in block 1014. The light strikesthe reflective mirrors inside DMD 1001. The reflected light forprojection leaves the surface of the DMD 1001 and travels into theoptional optics 1007 that operate to transmit the diffracted light asdescribed hereinabove. Together the integrated circuits 1011, 1003 and1015 cause the DMD 1001 and the optical components 1014, 1007 to outputthe diffracted light.

Example integrated circuits that can implement the circuit shown in FIG.10 include DMD controller ICs from Texas Instruments Incorporated. DMDcontroller ICs include, for example, the DLPC3430 DMD controller, andthe DLPC2601 ASIC device that can provide both digital and analogcontroller functions. Analog DMD controller devices from TexasInstruments, Incorporated include the DLPA2000 device. Laser controllerdevices can power on and off the laser 1009 or form pulses.

The DMD of FIG. 10 can be a DMD device from Texas InstrumentsIncorporated such as the DLP2010DMD, which is a 0.2-inch diagonal devicethat provides wide VGA (WVGA) resolution. The embodiments can use manyother DMD devices that are available from Texas InstrumentsIncorporated.

FIG. 11 depicts an operation using a system 1100 to illustrate the useof diffraction patterns displayed on a DMD to create a particulardesired pattern. In FIG. 11, the components are similar to those shownin FIG. 7, and similar reference labels are used. For example, the DMDin FIG. 11 is 1103, similar to the DMD 703 in FIG. 7. In thisillustrative example, the system 1100 creates a pattern in a far fieldimage plane corresponding to the Texas Instruments logo. A processor,not shown for simplicity, controls the laser and the DMD. The laser 1105illuminates the DMD 1103. DMD 1103 has a diffraction pattern loaded intothe DMD array. The pattern diffracts the light and the light wavesleaving the DMD surface travel through an afocal lens 1107 that expandsthe light to enlarge the field of view. Afocal lenses 1107, 1108 areoptional. At a desired distance in the far field of view, the pattern1109 appears. This visible pattern is an interference pattern, so thepattern did not result from projecting an image using the DMD.

By sensing reflections from objects illuminated by the interferencepattern, an embodiment system can detect objects at a variety ofdistances from the source, from a few centimeters to one hundred or evenseveral hundred meters. Unlike a projection system with a focused imagedistance, the system 1100 can form arbitrary patterns at a variety ofdistances without the use of complex moving optical elements. In theembodiments, the diffraction patterns displayed at the DMD can bechanged and illuminated in a sequence to create a scan pattern atdifferent points in the field of view.

FIG. 12 depicts in a top view a block diagram for an example system1200. In FIG. 12, a laser or other illumination source 1205 fullyilluminates an array of micromirrors on DMD 1203. The angle of the beamfrom the laser to the DMD is determined by the tilt angles of the DMDchosen for the embodiment and by the desired path leaving the DMDsurface. The DMD 1203 can be any DMD device. At least one detectorsenses reflected light. Objects in the field of view illuminated by thescan pattern reflect the light back to the detector. This example usesmultiple detectors 1221, 1223, 1225, and 1227. Alternative examples usemore or fewer detectors. The detectors can receive reflections caused bydifferent parts of the scan pattern. In an alternative embodiment, asingle detector can scan different portions of the field of view andsense reflections due to different patterns. A single detector cancapture reflections from different parts of the scan pattern with timedivision. The detectors are photodetectors that can be anyphotosensitive device as described hereinabove. A processor 1235provides data to the DMD and controls the laser 1205. The processor 1235can include multiple custom or commercially available integratedcircuits as described hereinabove to control the data displayed usingthe DMD and the laser pulses that illuminate the DMD. An optionalstorage for diffraction patterns couples to the processor 1235, the“Diffraction pattern memory” 1237, and stores two-dimensional arrays fordisplaying diffraction patterns using the DMD.

FIG. 13 depicts in another top view diagram a system 1300 similar to thesystem 1200 in FIG. 12, now shown in a scan operation. For ease ofcomprehension, FIG. 13 uses similar reference labels for components inFIG. 13 that correspond to similar components in FIG. 12. For example,in system 1300 the DMD is 1303, while in FIG. 12 the DMD in system 1200is 1203. In FIG. 13, under control of the processor 1335, laser orillumination source 1305 outputs a beam of light. The light strikes theface of the DMD at an incidence angle such as 24 degrees to the surfaceof DMD 1303, which can have a 12 degree tilt angle, so that the beamexits the system 1300 at zero degrees. Referring back to the DMD mirrorillustration in FIG. 5A hereinabove, the micromirrors have an ON statetilt angle direction and a different OFF state tilt angle direction.Light reflected by the DMD will exit the surface of the DMD in differentdirections for ON and OFF states. In image projection systems, thesystem typically directs OFF state light to a light dump or thermal heatsink. In contrast to the conventional DMD projection systems, in theembodiments the OFF state beams form additional scan patterns andthereby increase efficiency. In FIG. 13, patterns form by both ON stateand OFF state reflections from the surface of DMD 1303. The On-statescan beam 1309 causes a first scan pattern in the field of view. Theefficiency of the first order pattern from the on state is approximately10%. If this On-state scan beam 1309 were the only one used forscanning, the total efficiency for the system 1300 would be about 10%.However, as described hereinabove, each diffraction pattern at the DMDdisplay results in two images in the field of view. FIG. 13 shows afirst order On-state conjugate beam 1311, which is the conjugate patternof the ON state beam 1309. Further, in this embodiment a scan patternuses the OFF state pattern. The OFF state beam will deflect from thesurface of the DMD 1303 at a different angle than the ON state beam dueto the differing tilt angles such as shown in FIG. 5A. In FIG. 13,Off-state scan beam 1315 leaves the DMD 1303 at a different angle thanthe On-state scan beam. The Off-state conjugate beam 1317 leaves the DMD1303 at another angle. Each of these four beams forms an individual scanpattern that creates reflections detected by a sensor. FIG. 13 showsfour sensors for efficient processing; these are detectors 1321, 1323,1325 and 1327. In the embodiments, diffraction patterns have about 50%of the mirrors in the ON state and about 50% of the mirrors in the DMDare in the OFF state for each pattern, to increase efficiency. In analternative arrangement, fewer sensors can sense reflections from thedifferent patterns in time-sharing operations. In some embodiments, onlysome of the four possible scan patterns are used. In alternativeembodiments, a single detector can be used that can detect reflectionsfrom more than one of the On-state, On-state conjugate, Off-state, andOff-state conjugate scan beams. A moveable single sensor can detectreflections from the different scan patterns in a time division scheme.

Also shown in FIG. 13 is the zero order beam 1319. As seen in theexample diffraction pattern image illustrated above in FIG. 8C, thediffraction pattern will always create a zero order component that is inthe center part of the image. Because this zero order component does notmove, it does not form a pattern used for scanning. In one embodiment, alight dump or reflector blocks the zero order beam so that it does enterthe field of view and cause any object reflections. In another exampleembodiment, the zero order beam reflects from a mirror positioned withthe DMD, and the reflection becomes a time reference. Using the distancetraveled to the mirror and the distance back to a sensor of the zeroorder beam provides a time reference for use in determiningtime-of-flight for other reflections.

By using the on state beam, the conjugate on state beam, the off statebeam and the conjugate off state beam, the total efficiency of thesystem can increase to approximately 40%. This efficiency is muchgreater than the nominal 10%-12% efficiency obtained by using the firstorder ON state beam alone. The increase in efficiency occurs by use ofthe DMD with an ON state and OFF state tilt as a diffractive element,and comes at no additional cost in terms of components and processing.

FIG. 14 illustrates the scan beams obtained using a DMD with a diamondpixel mirror arrangement as described hereinabove. Because the diamondpixel oriented micromirrors tilt about a vertical axis, the on state andoff state reflections coming off the mirror surfaces are horizontallydisplaced. Further, the conjugate on and off state beams are alsohorizontally displaced. FIG. 14 shows the four beams in an example scanpattern in a field of view. The pattern 1409 corresponds to the ON statefirst order scan pattern, the pattern 1411 corresponds to the conjugateON state first order scan pattern, the pattern 1417 corresponds to theOFF state first order scan pattern, and the pattern 1415 corresponds tothe OFF state conjugate first order scan pattern. Because the four scanpatterns are displaced horizontally across the field of view, the opticsneeded in a system to form this pattern can be simplified when using adiamond pixel oriented DMD. However, the system can use any DMD device.In a square pixel or Manhattan oriented DMD device, offset optics can beused to extend the field of view and to align the beam patterns from thevarious ON and OFF states and the corresponding conjugate states.

The embodiments can also perform adaptive scene scanning. In oneembodiment, an adaptive scene scan can increase the sampling density ofthe scan beam for a portion of a scene. In one example, adaptivescanning occurs when the system detects an object. The adaptive scancapability is possible because the pattern created in the field of viewadaptively changes simply by changing the diffraction pattern displayedusing the DMD, and illuminating the DMD. Further, the embodiments cancreate multiple beam patterns in the far field image plane with a singleillumination source by adaptively modifying the diffraction patternsdisplayed using the DMD. No additional hardware is required to createthese multiple beam patterns.

FIG. 15 shows a scan pattern 1501 in a field of view 1500. In thisexample, a raster scan pattern is shown. FIG. 15 shows robot arm 1503 inthe field of view. FIG. 15 shows a human 1505 walking towards the robotarm and in close proximity to the robot arm 1503. In FIG. 15, scanpattern 1501 begins at arrow 1502 and continues scanning across thescene and towards the bottom of the field of view. In an industrialapplication, a safety system can stop the operation of a robotic armwhen a person or another object approaches the robotic arm device. Herethe distance between the objects is of interest. When a human enters anarea considered too close to the robotic arm, the system can take actionby sounding audible alarms, enabling visual alarms such as lights orsigns, or stopping operation of the robot arm until the area is againfree from other objects or persons and the robot arm is again safe tomove.

FIG. 16 illustrates the operation of an embodiment method using a sceneadaptive scanning pattern to scan a field of view similar to the fieldof view of FIG. 15. Field of view 1600 includes a robotic arm 1607 and ahuman 1609 shown near the robotic arm 1607. A first scan pattern 1601 isa first raster scan pattern that covers a portion of the field of view.A second scan pattern 1603 covers a second portion of the field of view.In this example, the second scan pattern 1603 has a beam sample densitygreater than the first scan pattern 1601.

In operation, the scan pattern 1601 starts at position 1602 andprocesses through a portion of the field of view where no object wasdetected in a prior scan. The scan pattern 1603 begins at position 1604and processes through the area of the field of view where the roboticarm was detected. Because the second scan pattern 1603 is denser thanthe first scan pattern 1601, it is of higher resolution (more coverage)than the lower resolution pattern of 1601. By changing the diffractionpatterns displayed using the DMD, the sample density adjusts to get moreinformation in areas where objects are detected in proximity to otherobjects, or for other reasons. The DMDs in the embodiments provide ascene adaptive scan resolution without the need for any additionalcomponents or without any other changes to the existing system. Thediffraction patterns can create multiple scan beams in the field of viewwith only changes to the diffraction patterns displayed using the DMD,and these changes can be in response to the detection of objects to formscene adaptive scanning patterns.

FIG. 17 depicts in a block diagram a top view of another systemembodiment. The reference labels used in FIG. 17 are similar to those inFIG. 13 for components that have similar functions, however in FIG. 17the reference labels start with “17,” for ease of comprehension. Forexample, DMD 1703 is similar to DMD 1303 in FIG. 13. In system 1700, aprocessor 1735 provides diffraction patterns to a DMD 1703 and controlsillumination of laser 1705. An optional memory 1737 can storediffraction patterns as described hereinabove. Each of the scan beams1709, 1711, 1715, and 1717, the On state scan beam; the Conjugate Onstate Scan beam; the Off state Scan beam; and the Off state ConjugateScan beam; has two scan patterns such as those shown in FIG. 16. Thefirst scan pattern shown as “1” in 1709 is of coarse resolution, whilethe second scan pattern “2” provides a finer resolution scan in an areaof interest. Note that the two scan patterns labeled 1 and 2 in the scanbeam 1709 are produced simultaneously. The diffraction patterns are notalternating in time. Instead, multiple scan patterns can be produced atthe same time simply by modifying the diffraction patterns displayedusing the DMD. The sample density can be greatly increased as a result.The detectors 1721, 1723, 1724, 1725, 1727, receive reflections fromobjects such as 1731. FIG. 17 also includes more than four detectors. Inthe embodiments, additional detectors can allow for faster processingand more coverage. In the embodiments, first and second scan patternscan display simultaneously. Additional detectors can match thesimultaneously displayed scan patterns thus increasing the effectivescan rate. Alternatively, additional embodiments can use fewerdetectors.

FIG. 18 depicts a flow diagram for an example method 1800. In FIG. 18,the method begins at step 1801, where a desired image pattern isdetermined. This image will appear in the field of view. At step 1803,the method performs an inverse Fourier transform. Fast Fouriertransforms such as discrete Fourier transforms can perform the inverseFourier transform. At step 1805, the method performs a quantization orbinarization step. Because the DMD is a binary amplitude modulator withtwo states, ON and OFF, the method quantizes the inverse Fouriertransform for use with the binary format of the DMD. In step 1807, themethod subsamples the quantized diffraction pattern formed in step 1805to match the particular DMD mirror orientation in the system. For adiamond pixel device, a different subsampling applies than that for asquare pixel device. At step 1809, the diffraction pattern is displayedusing the DMD. At step 1811, the method illuminates the diffractionpattern by the light source to form the image pattern. The image patternforms as wavefronts of diffracted light constructively and destructivelyinterfere as the wavefronts move away from the DMD, and the desiredpattern appears in the field of view. Step 1813 shows an optionalstorage step. Diffraction patterns can be stored in a pattern memory forlater retrieval and display. Alternatively, the method can compute theDMD diffraction patterns as needed in real time. Algorithms also existthat generate periodic diffraction patterns and that can be performedquickly without the use of Fourier transforms, and these algorithms canbe used with the embodiments.

FIG. 19 illustrates in a flow diagram a method 1900 for formingdiffraction pattern templates for use in the embodiments. In FIG. 19,the method begins at step 1901 where a desired scan pattern isdetermined. For example, the method can select a raster scan pattern. Atstep 1903, for each image in the pattern, the method performs an inverseFourier transform. Because a scan pattern is a sequence of images, themethod performs a plurality of inverse Fourier transforms. At step 1905,the method quantizes or performs binarization for each of the inverseFourier transforms to form a diffraction pattern sequence for the binaryDMD array. At step 1907, each of the quantized diffraction patterns issubsampled to map it to the DMD used in a particular embodiment. At step1909, the subsampled and quantized diffraction pattern sequence isstored in memory.

The method of FIG. 19 illustrates that the diffraction patterns can becomputed “off-line” or in a calibration operation during manufacture ofan embodiment system, and then the patterns can be stored for later use.In this approach, the system does not have to perform real timecomputations of the diffraction patterns during operation.

In FIG. 20, illustrates in a flow diagram a method 2000 for using thestored diffraction patterns to form a scan pattern. Beginning at step2001, a desired scan pattern is selected from a number of stored scanpatterns. At step 2003, the method retrieves the stored diffractionpatterns. At step 2005, a looping operation begins. For each diffractionpattern in a sequence needed to form the selected scan pattern, themethod displays the selected diffraction pattern using the DMD. At step2007, the method illuminates the DMD to form an image that is part ofthe scan pattern. At step 2009, the method detects reflections from anyobjects illuminated in the field of view. At step 2011, the methoddetermines distance to the objects using time-of-flight computations.The method continues looping through the sequence to continue scanningthe field of view by returning to step 2005.

The embodiments form light detection and distance measurement systemsuseful in a wide variety of applications. Mobile navigation andcollision avoidance systems, robotics, autonomous vehicle control,security, industrial automation, surveying, mapping, and meteorology areall applications for LIDAR systems including the embodiments. Thesystems use solid-state components without the need for mechanicalparts. Because DMD devices can operate even with a large percentage offailed micromirrors, the systems are inherently robust and reliable andare relatively low in cost. Use of a single illumination source and thelack of motors and rotors further reduces system cost, reduces systemmaintenance requirements, and increases reliability over conventionalapproaches.

Accordingly, in described examples, a system to output a patterned lightbeam includes a digital micromirror device having an array ofmicromirrors that each have an ON state and an OFF state, configured todisplay diffraction patterns that create at least one patterned lightbeam in a field of view. The system includes an illumination sourceconfigured to illuminate the array of micromirrors in the digitalmicromirror device. The system also includes a processor coupled to thedigital micromirror device and the illumination source, configured toprovide display diffraction patterns for display using the digitalmicromirror device, and configured to control the illumination source.At least one detector in the system detects light from the patternedlight beam reflected by objects in the field of view.

In a further example, the system includes the illumination sourcepositioned to illuminate micromirrors in the digital micromirror devicethat are in the ON state to cause an ON state light beam pattern in thefield of view and to cause a conjugate ON state light beam pattern inthe field of view. In another example, the system includes theillumination source positioned to illuminate micromirrors in the digitalmicromirror device that are in the OFF state to cause an OFF state lightbeam pattern in the field of view and to cause a conjugate OFF statelight beam pattern in the field of view.

In yet another example the detector includes a plurality ofphotodetectors arranged to detect reflections from objects illuminatedby light beam patterns in the field of view. In still another example,the detector includes a single detector configured to detect reflectionfrom objects caused by different light beam patterns in the field ofview. In an alternative example, the system further includes diffractionpattern memory configured to store diffraction patterns for displayusing the digital micromirror device. In yet another example, in thesystem includes a digital micromirror device having an array oforthogonally oriented micromirrors that have a diagonal tilt axis. Instill another alternative example, the system includes a digitalmicromirror device that includes an array of diamond-orientedmicromirrors that have a vertical tilt axis.

In a further example, the system includes a processor that includes areal time diffraction pattern-generating algorithm for outputting datato the digital micromirror device to display diffraction patterns. Instill a further example, the system includes the illumination sourcethat is a laser illumination source or an infrared illumination source.In an alternative example, the system includes a plurality of lightbeams that extends from the digital micromirror device into a field ofview, the plurality of light beams corresponding to an ON state beam, anON state conjugate beam, an OFF state beam, and an OFF state conjugatebeam.

In another example embodiment, a method provides a sequence of patternedlight beams into a field of view using a digital micromirror device as adiffractive pattern source. The method begins by determining an imagepattern sequence; computing a sequence of diffractive imagescorresponding to the image pattern sequence; and for the sequence ofdiffractive images, determining a sequence of quantized diffractionpatterns. The method continues by mapping the sequence of quantizedimage patterns for display. The method continues by using the digitalmicromirror device, displaying the mapped sequence of quantizedpatterns; and for the mapped sequence of quantized diffraction patternsdisplayed using the digital micromirror device, illuminating the digitalmicromirror device to create the image pattern sequence.

In another example, the method includes storing the sequence ofdiffraction patterns in a diffraction pattern storage memory. In afurther example, the method includes determining a quantized diffractionpattern that simultaneously creates multiple beams in the field of view.

In an additional example, the method includes computing a sequence ofdiffractive images corresponding to the image pattern sequence includingapplying an inverse Fourier transform to image patterns in the imagepattern sequence.

In an alternative example, the method includes determining a pluralityof quantized patterns to form a plurality of diffraction patterns fordisplay using the digital micromirror device, corresponding to a scanbeam pattern; storing the plurality of diffraction patterns in adiffraction pattern storage memory; and retrieving the storeddiffraction patterns from the diffraction pattern storage memory. Themethod continues by using the digital micromirror device and displayingthe plurality of diffraction patterns using the digital micromirrordevice in a sequence; illuminating the diffraction patterns using thedigital micromirror device in the sequence to form a patterned scan beamin a field of view; and detecting scan beam light reflected from objectsin the field of view. In a further example, the method continues bydetermining a distance of objects in a field of view usingtime-of-flight calculations.

Another alternative method includes, after detecting objects in a fieldof view, modifying a selection of the diffraction patterns to create anew scan pattern having a first sampling density for a portion of thenew scan pattern and a second sampling density different from the firstsampling density for another portion of the new scan pattern. The methodcontinues by creating new diffraction patterns by computing a sequenceof new diffraction images corresponding to the new scan pattern,quantizing the new diffraction patterns; subsampling the quantized newdiffraction patterns for a digital micromirror device; displaying thesubsampled quantized new diffraction patterns using the digitalmicromirror device; and illuminating the digital micromirror device.

In still another example embodiment, a LIDAR system includes at leastone illumination source to illuminate a digital micromirror device withcoherent light; and a processor coupled to display diffraction patternsusing the digital micromirror device. The LIDAR system also includes atleast one detector configured to detect light reflected from objects ina field of view illuminated by a light beam pattern formed due to theilluminating of the diffraction patterns displayed using the digitalmicromirror device.

In a further example, the LIDAR system includes a plurality of detectorsarranged to detect light reflected from objects in the field of view dueto at least one of an ON state light beam, an ON state conjugate lightbeam, an OFF state light beam, and an OFF state conjugate light beamfrom the digital micromirror device. In an alternative example, theLIDAR system includes the processor coupled to adaptively change a scanpattern by changing the diffraction patterns displayed using the digitalmicromirror device, responsive to detecting a reflection indicating anobject in the field of view.

Modifications are possible in the described embodiments, and otherembodiments are possible that are within the scope of the claims.

What is claimed is:
 1. A system, comprising: circuitry configured toproduce a first control signal and a second control signal; anillumination source coupled to the circuitry, the illumination sourceconfigured to produce light responsive to the second control signal; anda spatial light modulator (SLM) having an array of pixels, the SLMcoupled to the circuitry and optically coupled to the illuminationsource, the array of pixels configured to modulate the light in adiffraction pattern responsive to the first control signal to: producean ON state light beam using ON state pixels of the array of pixels in afield of view; and produce an OFF state light beam using OFF statepixels of the array of pixels in the field of view.
 2. The system ofclaim 1, wherein the diffraction pattern further produces a conjugate ONstate light beam in the field of view.
 3. The system of claim 2, whereinthe diffraction pattern further comprises a conjugate OFF state lightbeam in the field of view, including by illuminating pixels having anOFF state in the SLM.
 4. The system of claim 3, further comprising atleast one detector configured to detect a reflection of the ON statelight beam and the OFF state light beam in the field of view.
 5. Thesystem of claim 4, wherein the at least one detector is multiplephotodetectors or a single detector.
 6. The system of claim 1, furthercomprising a memory configured to store information representative ofthe diffraction pattern.
 7. The system of claim 1, wherein the array ofpixels is: an array of orthogonally oriented pixels that have a diagonaltilt axis; or an array of diamond-oriented pixels that have a verticaltilt axis.
 8. The system of claim 1, wherein the circuitry is configuredto provide the first control signal responsive to a real timepattern-generating algorithm.
 9. The system of claim 1, wherein theillumination source is a laser illumination source or an infraredillumination source.
 10. The system of claim 4, wherein the at least onedetector is configured to detect the reflection of the ON state lightbeam, the conjugate ON state light beam, the OFF state light beam, andthe conjugate OFF state conjugate light beam.
 11. A method comprising:determining, by circuitry, an image pattern sequence; computing, by thecircuitry, a sequence of diffractive images for the image patternsequence; for the sequence of diffractive images, determining, by thecircuitry, a sequence of quantized patterns; mapping the sequence ofquantized patterns to produce a mapped sequence of quantizationpatterns; and instructing, by the circuitry, a spatial light modulator(SLM) to modulate light in the mapped sequence of quantized patterns toform the image pattern sequence in a field of view.
 12. The method ofclaim 11, further comprising: storing the sequence of quantized patternsin a memory.
 13. The method of claim 11, further comprising: determininga quantized pattern that simultaneously forms multiple beams in thefield of view.
 14. The method of claim 11, wherein computing thesequence of diffractive images includes: applying an inverse Fouriertransform to image patterns in the image pattern sequence.
 15. Themethod of claim 11, further comprising: determining quantized patternsto form the mapped sequence of quantized patterns for a patterned scanbeam; storing the mapped sequence of quantized patterns in a memory;retrieving the mapped sequence of quantized patterns from the memory;using the SLM, modulating the light in the mapped sequence of quantizedpatterns to form the patterned scan beam in the field of view; detectinga reflection of the patterned scan beam in the field of view; andresponsive to the detecting, determining a distance of an object in thefield of view using time-of-flight calculations.
 16. The method of claim15, wherein the image pattern sequence is a first image patternsequence, the sequence of diffractive images is a first sequence firstdiffractive images, and the sequence of quantized patterns is a firstsequence of quantized patterns, the method further comprising:responsive to the detecting: producing a second image pattern sequencehaving a first sampling density for a first portion of the second imagepattern sequence and a second sampling density different from the firstsampling density for a second portion of the second image patternsequence; computing a second sequence of diffractive images for thesecond image pattern sequence; for the second sequence of diffractiveimages, determining a second sequence of quantized patterns; subsampling the second sequence of quantized patterns; and using the SLM,modulating the light in the subsampled second quantized patterns to formthe second image pattern sequence in the field of view.
 17. A vehiclecomprising: a roof; and a LIDAR system on the roof, the LIDAR systemcomprising: circuitry configured to produce a first control signal and asecond control signal; an illumination source coupled to the circuitry,the illumination source configured to produce light responsive to thesecond control signal; a spatial light modulator (SLM) having an arrayof pixels, the SLM coupled to the circuitry and optically coupled to theillumination source, the array of pixels configured to modulate thelight in a diffraction pattern responsive to the first control signalto: produce an ON state light beam using ON state pixels of the array ofpixels in a field of view; and produce an OFF state light beam using OFFstate pixels of the array of pixels in the field of view; and at leastone detector configured to detect a reflection of the ON state lightbeam and the OFF state light beam in the field of view.
 18. The vehicleof claim 17, wherein the diffraction pattern is further configured to:produce a conjugate ON state light beam using ON state pixels of thearray of pixels in the field of view; and produce a conjugate OFF statelight beam using OFF state pixels of the array of pixels in the field ofview.
 19. The vehicle of claim 17, wherein the diffraction patternincludes a scan pattern, the circuitry is coupled to the at least onedetector, and the circuitry is configured to adaptively change the scanpattern by changing the scan pattern, responsive to the at least onedetector detecting the reflection of the diffraction pattern in thefield of view.
 20. The vehicle of claim 18, wherein the at least onedetector is configured to detect a reflection of the ON state lightbeam, a reflection of the conjugate ON state light beam, a reflection ofthe OFF state light beam, and a reflection of the conjugate OFF statelight beam.